Recapping power supply for Soundcraft 760 series 24 track tape machine

[nashkato]

i got the complete (167 pages ) owners & service manual for SCM380/760 .
Drop me a PM

 

[skaren]

i got the complete (167 pages ) owners & service manual for SCM380/760 .
Drop me a PM

Thank you for your offer but I managed to download that already. Understanding the content is another matter

 

[abbey road d enfer]

See my post on Gearslutz. It definitely sounds like a bias problem to me.
You do realise the Soundcraft is a POS? Thats why there arent many of them round. Even an MCI is a better machine!

Very rude comment! Many wonderful albums have been done with this machine (think Eurythmics). I agree it has some shortcomings in the mechanical dept, but sonically it does not leave much to be desired.
I tend to agree that the issue may come from the master oscillator being noisy, or a noisy power rail  common to all bias/erase amps.

 

[radardoug]

Yes I am very rude about it! The problem will not be a common rail problem. It will be on each card. Bias cards are tricky, getting into the area of r.f. rather than audio.  And the purity of the waveform is crucial to getting low noise and low distortion.

 

[abbey road d enfer]

the purity of the waveform is crucial to getting low noise and low distortion.

Absolutely! But I have never seen a distorted bias waveform generating hum. But a noisy rail can be an indirect source of noise in case the bias amplifier is de-tuned or has poor PS rejection, dues to worn-out caps, for example.

 

[radardoug]

If you listen to his samples there is no hum, just lots of noise.

 

[abbey road d enfer]

If you listen to his samples there is no hum, just lots of noise.

Ah, as always, wrong diagnosis from wrong description of symptoms...

 

[radardoug]

You know how it is, its hard to get good staff! ;D

 

[reverbperv]

Hey everyone,
I'm stuck on a power supply issue with my series 760 Mk III(? Blue one) I have the manual from music parts.com, however the PSU section blurred exactly what info I need to know. I have to replace caps, regulators, transistors, and a few rectifiers. The machine was given to me, J. French said the heads will outlive me, and has the remote. So if I can fix the PSU, I'll be happy as a Pope in the confessional. Anyone have a really clean scan of the 760 power supply section from the manual? Please!!!

As a side note, I'm also trying to get some info and parts for an MCI JH-114. The cabinet is badged with this number.  I thought that was the later transport number, but I was told that they did make a pure JH-114, until they were sued by Ampex. When you look at the audio cards from my machine and a 1200, the layout is almost identical. Components are the same, just different values to reflect the head impedances. I always find the oddball shit.

 

[Avidy]

There is a relay on the audio card that open circuits the erase head when a channel is not in record, to avoid current flowing when adjacent tracks are in record. (Transformer effect within the head stack.)
However poor contact here will cause a fizzing when the track is actually in record.
New relays fitted by Soundcraft fixed this problem for me back in 1980 something...

 

[DeluMinaTi]

I worked on one of these guys around 1980 or so in my Soundcraft
warranty days. I thought I still had a full shop manual in the archives
Haven't found it yet but I'll keep looking. As I remember this guy was
very modular and easy to work on for being in such a small package.

I did find some poop sheet info however for those not familiar
with the 760 .

GARY

Hi Gary
Mate I would be so grateful if you could find that manual..I have the music parts 167pg pdf available on the net but lots missing in that one...I have seen the proper full technical manual for the machine and looks like this...thanks
Allen